Fundamental Resonance Research Articles

A hybrid summation and multiplication displacement amplification mechanism for piezoelectric actuators

Abstract This paper reports a novel amplified piezoelectric actuator featuring compliant displacement amplification mechanism of hybrid summation and multiplication. The hybrid amplification mechanism uses the concept of nesting a pair of Scott–Russell linkages into a toggle linkage to realize the hybrid amplification functions of summation and multiplication. Also, compliant amplification mechanisms with double output ports are designed, enhancing the flexibility of designs and applications. The hybrid displacement amplification principle is mathematically explained in detail. It is demonstrated based on finite element simulations that the displacement amplification ratio, output stiffness and resonance frequency of the proposed hybrid amplification mechanism of summation and multiplication outperform those of the classic rhombus-type and bridge-type compliant mechanisms. The experimental testing results of a prototype show that the amplified piezoelectric actuator is capable of providing 315 μm strokes with the displacement amplification ratio of 16.2. The fundamental resonance frequency with piezoelectric stacks mounted is 1218 Hz. Comparison to typical designs in literature shows well comprehensive performances of statics and dynamics, verifying the advantages of such a hybrid amplification mechanism of summation and multiplication.

System Integration Design of High-Performance Piezo-Actuated Fast-Steering Mirror for Laser Beam Steering System.

This paper presents an innovative piezo-actuated fast-steering mirror (FSM) that integrates control design and system operation to improve the tracking performance of laser beam steering (LBS) systems. The proposed piezoelectric FSM is centered on two pairs of stacked actuators functioning in the tip-tilt direction via novel flexible hinges with strain-gauge sensors for position measurement. The suggested flexible hinge scheme allows the first fundamental resonance mode with the optical mirror to exceed 400 Hz while achieving an actuation range of ±5 mrad. Thus, the design offers a wider mechanical actuation range than conventional piezoelectric FSMs. Moreover, LBS systems that use fast-steering motion controllers should be robust against dynamic disturbances, such as periodic external vibrations. Such disturbances, inherently associated with the operating conditions for LBS systems, typically reduce the stability of the tip-tilt motion. To attenuate the effects of such disturbances, a high-precision control system is necessary for the tip-tilt motion. Therefore, a control method integrating a proportional-integral controller with an adaptive feedforward control (AFC) algorithm is outlined to enhance tip-tilt tracking performance during high-speed scanning, compared with conventional LBS systems. Based on experimental findings, the AFC algorithm boosted control performance under dynamic disturbances, such as sinusoidal vibrations with multiple frequencies.

Heating characteristic of electron Bernstein wave using high-field side X-mode injection in QUEST

Abstract A comparative investigation was conducted to assess the impact of high-field side (HFS) extraordinary (X) mode (HFS X) injection and low-field side (LFS) ordinary (O) mode (LFS O) injection of 8.2 GHz radio frequency (RF) power in the Q-shu University experimental steady-state spherical tokamak. In the case of the HFS X injection, the ratio of electron plasma frequency and RF frequency f pe / f RF was 1.3, indicating an overdense plasma, whereas in the LFS O injection, this ratio was 0.9. Distinctive features emerged in the electron temperature and density profiles between the two injection scenarios. In the HFS X injection, the profiles peaked between the fundamental electron cyclotron resonance (ECR) layer and the upper hybrid resonance layer. Conversely, in the LFS O injection, the peaks were situated near the 1st ECR layer. This implies effective excitation of the electron Bernstein wave (EBW) in the case of the HFS X injection, with the wave power being absorbed through the doppler-shifted ECR of the EBW. Density and temperature oscillations were observed only in the start-up phase of the HFS X injection, which may correlate with the presence of the left-hand cutoff of the X-mode. These findings will be contributed to understand the distinctive characteristics associated with plasma heating through EBW excitation in the HFS X injection.

Interaction of acoustic waves with spin waves using a GHz operating GaN/Si SAW device with a Ni/NiFeSi layer between its IDTs.

A two port surface acoustic wave (SAW) device was developed to be used for the control and excitation via spin waves (SW). The structure was manufactured using advanced nanolithography techniques, on GaN/Si, enabling fundamental Rayleigh interdigitated transducer (IDT) resonances in GHz frequency range. The ferromagnetic resonance of the magnetostrictive Ni/NiFeSi layer placed between the IDTs of the SAW device can be tuned to the SAW resonance frequency by magnetic fields. Using structures with finger and interdigit spacing of 170 nm and 100 nm, fundamental Rayleigh IDT resonance frequencies of 6.4 and 10.4 GHz have been obtained. Coupling of SAW to SW was demonstrated through transmission measurements at the fundamental Rayleigh frequencies in a magnetic field, μ0H from -280 to +280 mT, at different angles (θ) between the SAW propagation direction and the magnetic field direction. For the 6.4 GHz resonator a maximum decrease of about 1.2 dB occurred in |S21|, at μ0H = 30 mT and at θ = 45. Time-gated processing of the frequency domain raw data was used to remove the direct electromagnetic cross talk and triple transit effects. Nonreciprocity associated to the coupling was analyzed for the two SAW structures. The quantitative influence of the magnetic field strength on the phase of the transmission parameters is also presented.

Non-contact and non-invasive water level measurement outside metal pipes with electromagnetic acoustic resonance

Accurate measurements of water levels within metal pipes are vital, particularly in environments where thick-walled pipes serve as critical components, such as in nuclear facilities. Measuring water levels in pipes becomes more difficult under high temperatures and pressures. In response to this need, a method involving electromagnetic acoustic measurement is proposed. This method begins with a transducer emitting a high-frequency pulse designed for precise measurements of wall thickness, then calculates the resonance frequency using the time intervals between echoes. Finally, the transducer emits an excitation signal at the fundamental resonance frequency to measure the water level. At low water levels, the measurement is conducted by manually scanning along the pipes, utilizing varying energy losses. At high water levels, the resonance echo method is employed. Numerical simulations have demonstrated that this approach effectively improves signal amplitude, thereby ensuring the robustness of the measurement. Experimental results also demonstrated that the proposed method boosted the echo signal-to-noise ratio to approximately 15 dB. Additionally, it successfully detected water levels in both aluminum and stainless-steel pipes. Therefore, it is considered to be a highly efficient non-contact and non-invasive method to measure liquid levels in metal pipes, and it has proved to hold significant potential for engineering applications.

Transition delay in a Mach 6 boundary layer using steady blowing and suction strips

Direct numerical simulations (DNS) were carried out to investigate flow control for transition delay using steady blowing/suction strips at the wall of a flared cone at Mach 6 and zero angle of attack. For the numerical investigations of the transition control strategy, the flared cone geometry and the flow conditions of the experiments in the Boeing/Air Force Office of Scientific Research (AFOSR) Mach 6 Quiet Tunnel (BAM6QT) at Purdue University were chosen. For the DNS, transition was initiated by introducing random disturbances at the inflow of the computational domain, emulating ‘natural’ transition in wind-tunnel experiments caused by free-stream noise. In both wind-tunnel experiments and numerical simulations, streamwise ‘hot’ streaks were found on the surface of the flared cone, which are caused by a nonlinear interaction of an axisymmetric second-mode wave and a pair of oblique waves of the same frequency (‘fundamental resonance’). The objective of the flow control strategy proposed here is to delay the transition onset, and thus mitigate the negative consequences associated with the nonlinear transition stages, i.e. the development of hot streaks and large wall-pressure amplitudes that were observed in experiments and DNS. Our previous so-called ‘controlled’ transition simulations have shown that flow control using steady blowing and suction strips can lead to a significant delay of the hot streak development on the surface of the flared cone. The simulation results presented in this paper show that this flow control strategy remains effective, even in a natural transition scenario characterized by broadband disturbances.

Original Insights Into Rock Slope Damage Processes Until Collapse From Passive Seismic Monitoring

AbstractWe performed a passive seismic monitoring of the La Praz ∼14,000 m3 unstable slope (French Alps) spanning over 10 years. During the last 6 months prior to collapse, we detected a clear 24% decrease in the slope's fundamental resonance frequency, f0, caused by a reduction in overall rock mass stiffness. The combined study of f0 and slope deformation suggested the alternating importance of sudden brittle failure processes versus more ductile phases with possible sliding. Seismic monitoring revealed slope damage that remained ambiguous or undetected with ground surface deformation monitoring, and highlighted critical periods with intense damage. Only some of these critical damage periods could be related to clear external forcing factors such as intense rainfall episodes. These new insights into rock slope's structural condition at depth represent an asset for future monitoring systems. Surface deformation and passive seismic stiffness tracking combined could reveal active slopes with ongoing damage processes.

Comparative evaluation of wavelength-scanning Otto and Kretschmann configurations of SPR biosensors for low analyte concentration measurement

Abstract The growing demand for compound characterization has stimulated research, particularly in surface plasmon resonance technology. This technique monitors changes in the light-reflecting properties of a sample medium in close contact and in interaction with a plasmonic surface (typically a metal such as gold) due to shifts in the fundamental plasmon resonance of the surface. The Otto and Kretschmann configurations are commonly used in this method. When an analyte is expensive, scarce, or hazardous, it is advantageous to reduce the sample required for testing, making optimization of sample use interesting. This challenge requires trade-offs between sensitivity and LoD. This work compares two sensors in the indicated configurations designed for minimal analyte requirement (in this case, Ag nanoparticle suspensions) using the wavelength scanning technique. The results show that the Kretschmann configuration is the most efficient for characterizing nanoparticle suspensions due to its construction characteristics, ease of use, and the characteristics of the obtained response. The final arrangement is a quasi-point sensor that only requires 6μL of analyte and has a sensitivity of 4.17x10−4 RIU/λ (RIU is the refractive index unit). This study contributes to the exploration of advantages and limitations in the design and operation of SPR sensors. The work also underlies the need for future research to enhance the selectivity and versatility of these devices.

Exploring the effective implementation of population-based SHM in existing buildings. Part II: Damage-feature classification for decision-making

In the context of structural condition assessment, transfer learning methods overcome some of the difficulties associated with the paucity of information on the actual structural condition of a target structure. This study aims to associate the building’s response with a population of nominally identical buildings for which a form is derived from existing empirical models relating certain basic characteristics (e.g., structure height) with the fundamental resonance period. This paper presents a structural condition classification based on the measured resonance period of the target structure, presented as the Build’Health™ solution. First, damage thresholds are defined by the shift of the fundamental period, which is considered to be a damage-sensitive characteristic for a given building population form, derived from almost thirty published references. The implicit period variation due to certain weather conditions is also included. Multinomial logistic regression and Gaussian mixture models are then used to classify damage according to the performance levels used in earthquake engineering (i.e., Operational Condition, Immediate Occupancy, Life Safety and Collapse Prevention). A performance-based probabilistic framework using a traffic-light system (green-orange-red classification) is finally used to classify structural condition. The method is tested and validated on several buildings surveyed after weak to strong earthquakes with different structural conditions. We show the complementarity of combining transfer learning, which gives the actual state of the target specimen with respect to a nominally identical population form of buildings, with multinomial logistic regressions and Gaussian mixture models for operational condition-based decision-making defined by the measured resonance period. This manuscript is the second in a series aimed at developing the Build’Health™ operational method for assessing the condition of real buildings (Part I on damage detection using transfer learning and Part II on classification using Gaussian mixture models and multinomial logistic regressions) based on basic building information.

Mapping bedrock topography and detecting blind faults using the fundamental resonance of microtremor: a case study of the Pohang Basin, southeastern Korea

SUMMARY The Pohang Basin sustained the most extensive seismic damage in the history of instrumental recording in Korea due to the 2017 Mw 5.5 earthquake. The pattern of damage shows marked differences from a radial distribution, suggesting important contributions by local site effects. Our understanding of these site effects and their role in generating seismic damage within the study area remains incomplete, which indicates the need for a thorough exploration of subsurface information, including the thickness of soil to bedrock and basin geometry, in the Pohang Basin. We measured the depth to bedrock in the Pohang Basin using dense ambient noise measurements conducted at 698 sites. We propose a model of basin geometry based on depths and dominant frequencies derived from the horizontal-to-vertical spectral ratio (HVSR) of microtremor at 698 sites. Most microseismic measurements exhibit one or more clear HVSR peak(s), implying one or more strong impedance contrast(s), which are presumed to represent the interface between the basement and overlying basin-fill sediments at each measurement site. The ambient seismic noise induces resonance at frequencies as low as 0.32 Hz. The relationship between resonance frequency and bedrock depth was derived using data from 27 boreholes to convert the dominant frequencies measured at stations adjacent to the boreholes into corresponding depths to the strong impedance contrast. The relationship was then applied to the dominant frequencies to estimate the depth to bedrock over the whole study area. Maps of resonance frequency and the corresponding depth to bedrock for the study area show that the greatest depths to bedrock are in the coastal area. The maps also reveal lower fundamental frequencies in the area west of the Gokgang Fault. The results indicate a more complex basin structure than previously proposed based on a limited number of direct borehole observations and surface geology. The maps and associated profiles across different parts of the study area show pronounced changes in bedrock depth near inferred blind faults proposed in previous studies, suggesting that maps of bedrock depth based on the HVSR method can be used to infer previously unknown features, including concealed or blind faults that are not observed at the surface.

First experimental realization of a thermoacoustic-based flue-gas analyzer

Flue-gas analyzers are critical for various applications, including the optimization of combustion efficiency and air quality monitoring. While capable of accurately measuring gas concentrations, current sensors require frequent calibration, suffer short lifespans, and can be susceptible to inference from trace gases. In this report, we provide a first physical implementation of a thermoacoustic-based gas analyzer by investigating the sensitivity of a standing-wave thermoacoustic engine to variations in three different flue-gas components, CO2, O2, and N2. Experimentally measured shifts in both the onset temperature difference and the fundamental resonance frequency with varying gas compositions confirm the feasibility of a thermoacoustic system for flue-gas analysis. The presented data paves the way for further exploration of this innovative approach, offering an efficient and cost-effective acoustic-based alternative to existing flue-gas analysis methodologies.

On the resonance frequency of the irregular shaped visco-acoustic Helmholtz cavity problem

In this paper we develop a closed-form mathematical solution for the resonance frequency of the axisymmetric irregular shaped visco-acoustic Helmholtz cavity problem. The solution is based on a conformal mapping that transforms the governing visco-acoustic equations of motion for the irregular cavity geometry into a new domain described by a set of orthogonal curvilinear coordinates. These orthogonal curvilinear coordinates have an important characteristic relative to the transformation of the physical boundary: the mapped domain is constructed such that the locus of all points for the length-wise profile of the physical boundary coincides with a constant value for a (quasi radial) coordinate in the new mapped domain. In these orthogonal curvilinear coordinates we obtain an analytical solution for the visco-acoustic equations of motion and exactly satisfy the no-slip fluid boundary conditions over the irregular shaped cavity walls by matching the coefficients of an orthogonal Legendre polynomial series representation for the non-uniform velocity on the cavity walls. The mathematical solution is an approximation to the extent that the scale factors chosen for the mapping consist of strictly the mutual-coupling terms of the true scale factors. Thus we analyze some results to understand the correlation of the analytical solution frequency response spectra with numerical finite element analyses of the idealized boundary conditions with various irregular shaped cavity geometries. The results for fundamental resonance frequency were found to exhibit good correlation with the results of finite element analyses over a significant range of fluid properties with different irregular cavity geometries. As the primary motivation for the derivation stems from the lack of a rapid yet accurate alternative to computationally intensive MultiPhysics FEA in the formulation of acoustic trendlines for sensor development, the solution’s acoustic impedance was applied as dispersive loading in a simple lumped parameter model of a fluid identification sensor for comparison. The resulting acoustic trendlines of the reduced (5 DOF) model were found to exhibit good correlation with the results of the MultiPhysics FEA (>105 DOF). Thus the solution was found to enable a closed-form analytical method for rapid construction of parametric studies in the practical design of fluid analysis sensors based on complex resonant cavity geometries.

Self-propulsion of a periodically forced shape-deforming submillimeter gas bubble.

The self-propulsion (translational instability) of a gas bubble in a liquid undergoing parametrically induced axisymmetric shape distortion due to being forced by a temporally sinusoidal, spatially constant acoustic field is investigated. Employing a model which accounts for the nonlinear coupling between the spherical oscillations, the axial translation and shape deformation of the bubble, the parametric excitement of two neighboring shape modes by the fundamental resonance, at the same driving frequency is studied. It is shown that provided pertinent driving pressure threshold values are exceeded, the respective shape modes are excited on different timescales. The growth of the shape mode on the faster timescale saturates giving rise to sustained constant amplitude oscillations, while the growth of the shape mode on the slower timescale is both modulated and unbounded. During the growth of the second shape mode, growing, oscillatory bubble translation is also observed.

Mode coupling with Fabry–Perot modes in photonic crystal slabs

Abstract Fabry–Perot (FP) modes are a class of fundamental resonances in photonic crystal (PhC) slabs. Owing to their low quality factors, FP modes are frequently considered as background fields with their resonance nature being neglected. Nevertheless, FP modes can play important roles in some phenomena, as exemplified by their coupling with guided resonance (GR) modes to achieve bound states in the continuum (BIC). Here, we further demonstrate the genuine resonance mode capability of FP modes PhC slabs. Firstly, we utilize temporal coupled-mode theory to obtain the transmittance of a PhC slab based on the FP modes. Secondly, we construct exceptional points (EPs) in both momentum and parameter spaces through the coupling of FP and GR modes. Furthermore, we identify a Fermi arc connecting two EPs and discuss the far-field polarization topology. This work elucidates that the widespread FPs in PhC slabs can serve as genuine resonant modes, facilitating the realization of desired functionalities through mode coupling.

Magnetoelectric effect in a Metglas–langatate ring heterostructure for current sensing

The magnetoelectric (ME) effect was observed and investigated in a planar ring-type heterostructure containing mechanically coupled rings of magnetostrictive amorphous alloy Metglas and a piezoelectric single crystal langatate. The structure was excited by a circumferential ac magnetic field in the presence of a circumferential dc bias magnetic field. Due to the absence of demagnetization and the high acoustic quality factor of the langatate, a high ME field conversion coefficient of α E ≈ 53 V (Oe cm)−1 was obtained at the frequency 221 kHz of the fundamental radial acoustic resonance mode. The structure can be used as a non-contact ac or dc current sensor. The sensitivity of the structure to the ac current was 1.6 V A−1, whereas for the dc current it reached 4.2 V A−1.

Direct numerical simulation of mechanism and control of secondary instability induced transition in a supersonic boundary layer

Mechanisms and control of secondary-instability-induced-transition in a supersonic boundary layer are studied numerically via direct numerical simulation. The aim is to investigate and compare the transition mechanisms of fundamental, subharmonic, asymmetric subharmonic, and detuned resonances, and to control these secondary instabilities using a local wall cooling strip. The results indicate that the nonlinear interaction between the high-amplitude primary mode and low-amplitude secondary modes is the main contributor to transition. The mutual- and self-interactions of the primary and secondary modes generate other harmonic modes with laminar breakdown soon appearing. The asymmetric subharmonic resonance induces the earliest transition, while the fundamental subharmonic has the latest. Wall cooling effects are also studied. The results show that a lower wall temperature significantly suppresses the secondary instabilities, and steady modes become dominant and lead to obvious streamwise vortexes. Numerical data demonstrate that all secondary-instability-induced transitions result in fully developed turbulent boundary layers, as supported by the skin friction and scaled velocity profiles. The transition control cases indicate that the local wall cooling strip can significantly delay the transition by suppressing the growth of the primary mode. An upstream control strip is found to have a more obvious suppression effect. The fundamental and asymmetric subharmonic resonances are sensitive to the location of the local wall cooling strip and show a stronger transition delaying effect.

Effects of streamwise-elongated and spanwise-periodic surface roughness arrays on supersonic boundary-layer instability

We investigate the influence of streamwise-elongated and spanwise-periodic roughness arrays on the supersonic boundary-layer instability under the assumption of a high Reynolds number. The main focus is on the lower-branch viscous instability modes, and the spanwise spacing of the roughness arrays is taken to be comparable to the characteristic wavelength of the modes (which is on the triple-deck scale), so that most significant effects can be generated. The streamwise length scale of the elements is much greater than the spanwise length scale. The roughness height is determined by requiring the change of the wall shear to be O(1). The equations governing the nonlinear roughness-induced streaky flow are deduced from the standard triple-deck theory. These equations are parabolic in the streamwise direction and are solved using a streamwise marching method to characterize the evolution of streaky structures. The linear stability of the streaky flow is analyzed. By exploiting the asymptotic structure, the bi-global eigenvalue problem is reduced to a one-dimensional one, where the stability is found to be controlled by the spanwise-dependent wall shear. The reduced eigenvalue problem is solved numerically. The results show that roughness arrays inhibit instability modes with moderate frequencies but promote high-frequency modes. Roughness elements of greater height have stronger effects on the linear stability. The shape of roughness elements plays an important role. A significant feature, different from the subsonic case, is that fundamental and superharmonic resonance modes radiate sound waves spontaneously into the far field.

Sub‐MeV Electron Precipitation Driven by EMIC Waves Through Nonlinear Fractional Resonances

AbstractElectromagnetic ion cyclotron waves in the Earth's outer radiation belt drive rapid electron losses through wave‐particle interactions. The precipitating electron flux can be high in the hundreds of keV energy range, well below the typical minimum resonance energy. One of the proposed explanations relies on nonresonant scattering, which causes pitch‐angle diffusion away from the fundamental cyclotron resonance. Here we propose the fractional sub‐cyclotron resonance, a second‐order nonlinear effect that scatters particles at resonance order n = 1/2, as an alternate explanation. Using test‐particle simulations, we evaluate the precipitation ratios of sub‐MeV electrons for wave packets with various shapes, amplitudes, and wave normal angles. We show that the nonlinear sub‐cyclotron scattering produces larger ratios than the nonresonant scattering when the wave amplitude reaches sufficiently large values. The ELFIN CubeSats detected several events with precipitation ratio patterns matching our simulation, demonstrating the importance of sub‐cyclotron resonances during intense precipitation events.

Excitation and evolution of radiating modes in supersonic boundary layers. Part 1. Fundamental resonance with impinging sound waves

Excitation and evolution of radiating modes in supersonic boundary layers. Part 1. Fundamental resonance with impinging sound waves

Vibration response of in-vacuo tuneable structured fabrics

This paper presents a first survey on the vibration response of beam-like specimens formed by a vacuum plastic bag with single-layer or double-layer 3D-printed structured fabrics encompassing spherical-octahedra, octahedra and cubes truss-like rigid elements. The study reports a comprehensive analysis of the bending stiffness and energy dissipation properties with respect to the level of vacuum as well as the type and number (single or double) of overlapped fabrics. In this context, it first presents a quasi-static analysis of the bending stiffness and energy dissipation of the specimens. Then, it provides a comprehensive overview of the specimens dynamic properties with respect to measurements of the dynamic stiffness frequency response function and with reference to measurements of hysteresis loops at three characteristic frequencies, namely below, at and above the fundamental bending resonance frequency of the beam-like specimens. The study shows that the bending stiffness and thus the fundamental bending resonance frequency of the specimens can be suitably varied by increasing the level of vacuum in the bags. The specimens made with cubic mails show the highest bending stiffness and fundamental resonance frequency. Also, the specimens with double layer mails show much higher bending stiffness and fundamental resonance frequency. The level of vacuum has little effect on the energy loss, which, in general, is characterised by rather low loss factors. This suggests that once the fabric jams, there is little friction between the particles and the principal damping mechanism is offered by the material energy dissipation in the unit particles.